Metal powders

ABSTRACT

In the production of B type carbonyl nickel powder, B powder having a desired low bulk density is obtained with process wherein the fine particles suspended in the exit gases from the decomposer are kept separate from the main product while operating conditions in the decomposer are controlled to avoid detrimental accumulation of a fluffy powder layer on decomposer walls.

United States Patent 1 1 u n Llewelyn l Nov. 1 l, 1975 l5 l METALPOWDERS 2.674.538 4mm Beller et al "is/2 AA [75] Inventor: David MyersLlewelynq Surnhelenq 3.694186 )J l97 Lle\\el \n 75/} AA Wales PrimaryE.\'um!'m'rW. Stallard [73] Asslgnee' 2:1 $g?: Compan" Almrm'y.Age/11.01- Firm-George N. Ziegler; Ewan C.

" MacQueen; Raymond J. Kenny [22] Filed: Ma 6. 1974 [ll] Appl. No:467.127

[57] ABSTRACT [30] Foreign Application Priority Data in the productionof B type carbonyl nickel powder. B

May 15. 1973 United Kingdom 22% /73 powder having a desired low bulkdensit is obtained with process wherein the fine particles suspended in[52] U 5 (1| H 75/5 75/5 AA the exit gases from the deeomposer are keptseparate [51] [m CL H 322 9/00 from the main product while operatingconditions in [53] Fi ld f S h 75/ 5 AA the decomposer are controlled toavoid detrimental accumulation of a fluff powder layer on decomposer[56] References Cited Walls- UNITED STATES PATENTS 2.663.630 12/1953Schlecht et al, 75/.5 AA 10 Claims No Drdungs METAL POWDERS The presentinvention relates to carbonyl nickel powder and to production ofcarbonyl nickel powder by thermal decomposition of nickel carbonylvapour in the hot free space of a decomposer.

The production of carbonyl nickel powder by thermal decomposition hasbeen carried out on an industrial scale for many years. The form ofdecomposer commonly used consists of a substantially cylindrical vesselwith heated walls mounted with its axis vertical, the carbonyl vapourbeing introduced at the top and the powder falling into the bottom,where it is collected and discharged. The carbon monoxide formed duringthe decomposition, together with any other gases introduced with thecarbonyl, also leave the decomposer at the bottom. These gases carrywith them some very fine powder in suspension which is separated andreturned to the bottom of the decomposer.

It is well-established that according to the conditions of temperature.the concentration and feed rate of carbonyl, and the presence or absenceof diluent gases, e.g., carbon monoxide, the powder produced may assumeone of two forms. These are the so-called A carbonyl nickel powder,which consists of discrete particles, and the so-called B powder, whichconsists of agglomerates of interlocking filaments or chains ofinterconnected (aggregated) particles. B powder has a low bulk density,generally less than 1.5 g/ml, and a microscopic appearance of smallspongy flakes. The size of the aggregates of particles making up thechains can vary widely.

The present invention relates only to processes in which B powder isproduced.

The use of low rates of carbonyl input and relatively low decompositiontemperatures leads to the formation of A powder while at higher inputrates and higher decomposition temperatures B powder is obtained, thebulk density of the B powder decreasing as the input rate ordecomposition temperature is increased. The higher the rate of carbonylinput or the decomposition temperature, the higher must be the walltemperature of the decomposer, particularly in the upper portion wheremost of the decomposition occurs, in order to introduce the requisitequantity of heat for the decomposition. This leads to difficulties whenB powder of very low bulk density, e.g., less than 1 g/ml (grams permillilitre) or even less than 0.8 g/ml, is required, since at high walltemperatures part of the large amount of carbonyl introduced tends todecompose near or even on the walls, so that a layer of fluffy powderbuilds up on the walls. This interferes with heat transfer through thewalls, and the plant must be periodically shut down in order to removeit. This is an inconvenient, dirty and time-consuming procedure.

In accordance with the present invention, B powder having a given lowbulk density is obtained with a lower carbonyl input or decompositiontemperature, and thus a lower wall temperature, with a carbonyldecomposition process wherein the fine particles suspended in the exitgases from the decomposer are kept separate from the main product.

This is surprising, since in B nickel powder a low particle size hasbeen associated with a low bulk density. On this basis the finesfraction having a lower Fisher particle size than the main product wouldbe expected to have a lower bulk density, and thus it would be expectedthat removal of this fines fraction from the system would raise the bulkdensity of the product. However it is surprisingly found that the fines,although having a lower Fisher value, have higher bulk density than themain product and that their removal from the system correspondinglydecreases the bulk density of the remainder of the powder. This in turnmeans that a main product (less the fines) having the same bulk densityas that hitherto obtained with incorporation of the fines can beobtained at a lower carbonyl input rate than hitherto.

In the process of the present invention for the production of B typenickel powder by the thermal decomposition of nickel carbonyl in adecomposer with or without the presence of a diluent gas, the rate ofinput of nickel carbonyl, the decomposition temperature, and the amountof any diluent gas introduced are correlated to provide that fluffynickel powder is not deposited on the heated walls of the decomposer,and fine nickel powder suspended in gases leaving the decomposer isrecovered separately, c.g., by filter, from the B type nickel powdersettling at the bottom of the decomposer.

Operating in this way not only enables B nickel powder to be obtainedwith a larger particle size for a given bulk density, but also enablespowders having unusually low bulk density, i.e., less than 1 g/ml, e.g.,0.8 g/ml, or less than 0.8 g/ml, preferably less than 0.5 g/ml and evenas low as 0.3 g/ml or less, to be obtained on a practical industrialscale. It is also found that at any given bulk density the powderproduced exhibits substantially less shrinkage on sintering than thepowder hitherto produced. Generally speaking, the fine particlesrecovered from the gases have :1 Fisher particle size of less than 2 pm,(microns) e.g., from 1.5 to 1.9 pm, and amount to from 10 to 17%, e.g.,about 15%, by weight of the total amount of powder produced.

The nickel carbonyl vapour fed to the decomposer is advantageouslydiluted, preferably with carbon monoxide or other inert diluent gas, sothat carbonyl concentration is preferably in the range of 10 to by volume of the total gas entering the decomposer. In addition it isadvantageous to introduce as a diluent a small amount of an agent forpromoting solid nuclei formation for the powder, preferably oxygen, forthe purpose of reducing the shrinkage on sintering without substantiallychanging the bulk density, as described in US. Pat. No. 2,844,456.Preferably, oxygen is introduced in an amount of from 0.01 to 0.06% byvolume of the total gas entering the decomposer, but larger amounts, upto not more than 0.1%, can be used, though these tend to lower theFisher value of the powder.

By way of example, B nickel powder was produced by the decomposition ofnickel carbonyl vapour mixed with carbon monoxide in a decomposerconsisting of an upright cylindrical vessel 2m (metres) in diameter and10m high, the walls of which were externally heated electrically. Theinternal temperatures were measured by means of thermocouples mounted ona vertical axis 20.3 cm from the walls at various levels, and the walltemperature was measured at various levels by thermocouples mounted inthe walls, three thermocouples being placed at each level apart aroundthe circumference of the wall.

Two series of tests were carried out. In the first series the finepowder separated from the exit gases was returned to the bottom of thedecomposer. In the second series, which are examples according to theinvention,

the fine powder was recovered separately from the powder settling at thebottom of the decomposer. The internal and wall temperatures measured asdescribed above were as set forth in the following Table l, the internaltemperatures being the same in the two series of 5 the tests but thewall temperatures in the upper part of the decomposer being lower in thesecond series.

Belovtop of decomposer The operating conditions in each series of testsare set forth in Table II infra, together with the bulk density andFisher particle size of the powder produced, which in each case was Bpowder.

4 loosely filled into a covered graphite-coated mould, flushed withnitrogen, and heated for minutes at 900C. under flowing hydrogen.

Powder produced by the process of the invention is particularly usefulfor the production of sintered supports for the plates of nickelalkaline batteries. This is due. inter alia, to the fact that separationof the fines according to the invention reduces the linear shrinkage ofthe powder produced according to the invention, on sintering, resultingin high porosity values and reduced sinterability.

Further, and of surprise, it was found that the fine particles have aremarkably low carbon content, preferably not more than 0.03% by weightand generally about 0.02%. compared with 0.l2 to 0.2% for the balance ofthe powder. The fine powder obtained with the invention has a highshrinkage on sintering typically of about and is particularly useful formaking sintered filters. The fine particles can be transformed intoflake fonn by mechanical treatment and in this form can be used as aselective light reflecting means in graphic displays actuatedmagnetically to provide visible patterns.

In both series the input gases in each test included 0.06% by volume ofoxygen.

In the tests of Series I, nickel powder accumulated on the heated wallsof the decomposer as a fluffy deposit and this powder appeared in themain product, whereas with the examples of Series ll there was noevidence of fluff in the product and, by inference, not on the wall ofthe decomposer.

Preferably, in the process according to the invention the rate of nickelcarbonyl input is in the range of from 70 to 1 17 m /h (cubic metres perhour), that is to say a total gas input in the range of from 500 to 650m /h with the concentration of nickel carbonyl in the range of from 14%to l8% by volume of the total gas entering the decomposer, and thetemperature of the inner wall of the decomposer is in the range of from400 to 500C. and advantageously not greater than 470C.

The diminished tendency of the powder to shrink on sintering when thefine particles are excluded is shown by the following results, in Tablelll, of comparative tests for typical batches of nickel powder madewithout separation of fines (contra to the invention) and withseparation of fines (examples according to the invention).

TABLE lll Fines separated Fisher size (pm) Fines not separated Fishersize (pm) Bulk density lg/ml) Bulk density (g/mll Linear shrinkage(7r)Linear shrinkage ('1 l Although the present invention has been describedin conjunction with preferred embodiments, it is to be understood thatmodifications and variations may be resorted to without departing fromthe spirit and scope of the invention as those skilled in the art willreadily understand. Such modifications and variations are considered tobe within the purview and scope of the invention and appended claims.

I claim:

1. In a process for the production of B type nickel powder by thethermal decomposition of nickel carbonyl in a decomposer with or withoutthe presence of a diluent gas, wherein the rate of input of nickelcarbonyl, the amount of any diluent gas introduced and the decompositiontemperature are controlled in correlation to provide that fluffy nickelpowder is not deposited on the heated walls of the decomposer, theimprovement comprising: recovering separately the fine nickel powdersuspended in exit gases leaving the decomposer and maintaining therecovered fine nickel powder and the B type nickel powder that settlesat the bottom of the decomposer separate from'each other, and therebyproviding a B powder product characterized by a bulk density less thanone gram per millilitre while avoiding deposition of fluffy nickel onthe decomposer walls and in addition providing a fine nickel powderproduct characterized by a Fisher particle size less than the Fisherparticle size of said B powder prod act and a bulk density greater thanthe bulk density of said B powder product.

2. A process according to claim 1 wherein the nickel carbonylconcentration is in the range of l0% to by volume of the total gasentering the decomposer.

3. A process according to claim I utilizing a diluent gas comprising anagent for promoting solid nuclei formation for the powder.

4. A process according to claim 3 wherein the promoting agent is oxygenin an amount up to 0.1% by volume of the total gas entering thedecomposer.

5. A process according to claim 4 wherein the amount of oxygen is 0.01to 0.06%.

6. A process according to claim 1 utilizing diluent gas comprising aninert gas, with or without a promoting agent gas.

7. A process according to claim 6 wherein the inert diluent is carbonmonoxide gas.

8. A process according to claim 1 wherein the rate of nickel carbonylinput is 70 cubic meters per hour to l 17 cubic metres per hour and thetemperature of the inner wall of the decomposer is 400 to 500C.

9. A process as set forth in claim I for the production of B type nickelpowder by the thermal decomposition of nickel carbonyl in a decomposer.with or without the presence of a diluent gas wherein the walltemperature of the decomposer vessel is 420 to 470C. and the rate ofinput of nickel carbonyl is equivalent to 77 cubic metres per hour toI00 cubic metres per hour into a two metre diameter decomposer vessel.

10. A process as set forth in claim I having a diluent comprising oxygenwherein the nickel carbonyl input rate, the decomposition temperature,the amount of diluent gas and the separate recovery of powder suspendedin exit gases are controlled in mutual correlation to provide a finesproduct characterized by a carbon content up to 0.03%, a Fisher particlesize up to L9 microns and a shrinkage on sintering typically about 257:.

1. IN A PROCESS FOR THE PRODUCTION OF B TYPE NICKEL POWDER BY THETHERMAL DECOMPOSITION OF NICKEL CARBONYL IN A DECOMPOSER WITH OR WITHOUTTHE PRESENCE OF A DILUENT GAS, WHEREIN THE RATE OF INPUT OF NICKELCARBONYL, THE AMOUNT OF ANY DILUENT GAS INTRODUCED AND THE DECOMPOSITIONTEMPERATURE ARE CONTROLLED IN CORRELATION TO PROVIDE THAT FLUFFY NICKELPOWDER IS NOT DEPOSITED ON THE HEATED WALLS OF THE DECOMPOSER, THEIMPROVEMENT COMPRISING: RECOVERING SEPARATELY THE FINE NICKEL POWDERSUSPENDED IN EXIT GASES LEAVING THE DECOMPOSER AND MAINTAINING THERECOVERED FINE NICKEL POWDER AND THE B TYPE NICKEL POWDER THAT SETTLESAT THE BOTTOM OF THE DECOMPOSER SEPARATE FROM EACH OTHER, AND THEREBYPROVIDING A B POWDER PRODUCT CHARACTERIZED BY A BULK DENSITY LESS THANONE GRAM PER MILLILITRE WHILE AVOIDING DEPOSITION OF FLUFFY NICKEL ONTHE DECOMPOSER WALLS AND IN ADDITION PROVIDING A FINE NICKEL POWDERPRODUCT CHARACTERIZED BY A FISHER PARTICLE SIZE LESS THAN THE FISHERPARTICLE SIZE OF SAID B POWDER PRODUCT AND A BULK DENSITY GREATER THANTHE BULK DENSITY OF SAID B POWDER PRODUCT.
 2. A process according toclaim 1 wherein the nickel carbonyl concentration is in the range of 10%to 80% by volume of the total gas entering the decomposer.
 3. A processaccording to claim 1 utilizing a diluent gas comprising an agent forpromoting solid nuclei formation for the powder.
 4. A process accordingto claim 3 wherein the promoting agent is oxygen in an amount up to 0.1%by volume of the total gas entering the decomposer.
 5. A processaccording to claim 4 wherein the amount of oxygen is 0.01 to 0.06%.
 6. Aprocess according to claim 1 utilizing diluent gas comprising an inertgas, with or without a promoting agent gas.
 7. A process according toclaim 6 wherein the inert diluent is carbon monoxide gas.
 8. A processaccording to claim 1 wherein the rate of nickel carbonyl input is 70cubic meters per hour to 117 cubic metres per hour and the temperatureof the inner wall of the decomposer is 400* to 500*C.
 9. A process asset forth in claim 1 for the production of B type nickel powder by thethermal decomposition of nickel carbonyl in a decomposer, with orwithout the presence of a diluent gas, wherein the wall temperature ofthe decomposer vessel is 420* to 470*C. and the rate of input of nickelcarbonyl is equivalent to 77 cubic metres per hour to 100 cubic metresper hour into a two metre diameter decomposer vessel.
 10. A process asset forth in claim 1 having a diluent comprising oxygen wherein thenickel carbonyl input rate, the decomposition temperature, the amount oFdiluent gas and the separate recovery of powder suspended in exit gasesare controlled in mutual correlation to provide a fines productcharacterized by a carbon content up to 0.03%, a Fisher particle size upto 1.9 microns and a shrinkage on sintering typically about 25%.